1. Field of Invention
The present invention relates to a total artificial heart which includes opposing pumping compartments, each having a pumping chamber and blood chamber confined within a heart enclosure. More particularly, the present invention relates to an improved single septum and coupled diaphragm configuration which separates the respective configuration compartments.
2. Prior Art
Increased effort over the last decade to generate an effective total artificial heart has resulted in numerous variations in housing, chamber, valve, and diaphragm design, placement relationship for the respective left and right ventricle, improved drive systems and numerous other technical enhancements intended to generate a reliable total artificial heart. Ultimately, however, success of the total artificial heart will rest primarily on its predictability and long-term survivability within the patient. Such long term use depends on the ability of the constantly oscillating diaphragms to perform their function of drawing blood within a blood chamber and expelling it to establish circulation to maintain life-sustaining circulation. In fact, many of the design features for various ventricles are specifically generated to enhance the survivability and reliability of the blood pumping diaphragm.
One of the more common heart designs involves the use of a pumping chamber which relies on a rigid wall or base and an attached flexible diaphragm and which is extended and retracted by reason of positive and, if necessary, negative pneumatic pressure applied through a connecting drive line to one side of the diaphragm. An opposing side of this diaphragm forms a partial, interior wall of a blood chamber, corresponding to the pumping ventricle of the natural heart. The use of a rigid wall in the pumping chamber forces the more flexible diaphragm to extend away from the wall in response to pneumatic pressure.
One limiting factor of efficiency for this total artificial heart system is a requirement that the diaphragm be protected against localized stress which weakens the diaphragm and eventually results in failure. Early heart designs utilized a body having a spherical configuration wherein the pumping diaphragm assumed a retracted position into a somewhat hemispherical shell, forming the concave side of a filled blood chamber. Upon positive pressure through a drive line, the pumping membrane expanded and inverted itself to a convex hemispherical configuration, reducing the volume of the blood chamber and forcing the blood to exit through a valved outlet. During the course of its traverse from a retracted position in full hemispherical shape to the extended, convex configuration, the diaphragm passes through an intermediate, transitory condition wherein multiple uni- and biaxial folds occur within the diaphragm structure. A primary challenge of diaphragm design has been to minimize such folding and to reduce recurrence of common fold patterns which eventually weaken the affected area of the diaphragm. One area of focus in prior art techniques has involved design of a diaphragm which avoids predictable or repetitive fold pattern, and favors a random folding experience which protects the elastomer against localized stress.
In most cases, conventional design of the semi-rigid wall of the pumping chamber has retained a concave configuration to facilitate collapse of the diaphragm into a retracted position. See for example, U.S. Pat. Nos. 4,427,470 and 4,573,997 showing various prior art ventrical configurations having a separate rigid wall for each ventricle.
U.S. Pat. No. 4,750,903 represents a shift in diaphragm design for a TAH wherein a single, intermediate rigid septum or wall forms a base for each opposing ventricle. Furthermore, the direction of pumping movement for the diaphragm is lateral or somewhat parallel with respect to this wall, rather than normal thereto. According to this design, the pumping membrane is configured to collapse and extend to and from a vertical support which projects upward from the rigid base, resulting in diaphragm movement in a lateral orientation, as opposed to the conventional pattern of collapsing the diaphragm to or extending it away from the rigid wall.
Although this strategy of diaphragm design avoids adverse folding of the diaphragm, it introduces a new range of problems, including oriented drive lines which enter from a remote position with respect to the rigid base, in contrast with the more conventional approach of having the drive line establish pressure at the base and diaphragm juncture. This necessitates use of a central support column to maintain the drive line and diaphragm in a separated position from the rigid base.
Other problems will be apparent to those skilled in the art, including not only technical problems within the artificial heart structure, but thoracic space limitations relative to opposing drive line connections on opposite sides of the total artificial heart structure. When viewed in comparison with earlier prior art artificial ventricles, the trends in design generally appear to be raising unnecessary new problems, rather than solving old ones. What is needed is a simple artificial heart structure that enhances reliability and efficiency, while retaining structural simplicity.